The output signals of microphones are usually amplified by an amplifying circuit before they are forwarded, for example, to an analog/digital converter or other downstream amplifying units. In the widely used two-wire ECM (electret condenser microphone) microphones, the microphone features an output terminal for outputting a voice signal and a reference voltage terminal for applying a reference voltage. The output terminal is generally connected to a voltage source and downstream signal processing circuits such as, for example, amplifying circuits or analog/digital converters via a coaxial cable. Since ECM microphones merely feature two terminals, microphones of this type are used, for example, in connection with headsets, wherein a shielded wire (coaxial cable) can be used for transmitting the voice signals.
In addition to ECM microphones, MEMS microphones are also used. Three terminals are generally provided on the housing of a MEMS microphone. One terminal is provided for applying a supply voltage, another terminal is provided for contacting a reference voltage, and another terminal is provided for outputting the output signal. In contrast to ECM microphones, MEMS microphones therefore feature an additional terminal, namely the terminal for applying the supply voltage.
The external supply voltage is respectively used for operating other amplifying circuits integrated into the microphone and for generating a bias voltage for the microphone membrane of the MEMS microphone. This bias voltage is generally slightly higher than the voltage at the output terminal of the MEMS microphone. In order to operate the MEMS microphone, the terminal for applying the supply voltage therefore is usually connected to an external supply voltage source.
Due to the fact that these microphones feature, in comparison with an ECM microphone, an additional terminal for applying the supply voltage, the use of MEMS microphones is frequently associated with a higher wiring complexity, higher production costs, and the use of a larger portion of the chip surface. In addition, an exchange between the different types of microphones is generally complicated or in the most instances impossible due to the lacking compatibility with respect to the terminals.